Some years ago, a female manager at a large global bank based in New York received a curious e-mail. "Nice shoes," it read. Her 4-inch black suede heels had obviously impressed the sender, a male senior partner. "He had exceptional taste," she recalls with a chuckle. "I thought to myself: I'll file that away."

The partner was a decision-maker in the company and a good person to have on her side. From that day on, whenever she had a presentation and knew he'd be in the room, she paid special attention to her footwear — never flats, always stilettos that added another four inches to her already-striking height of 5'8". "Flirting? I call it efficiency," she says.

Flirting, after all, is one of the oldest tricks in the book. But how do you use it to your professional advantage without crossing the line or inviting unwanted advances?

"Using flirtation is just smart," says Nicole Williams, author of "Girl on Top: Your Guide to Turning Dating Rules into Career Success." "If you need someone's help, use the tools available to you. It's naive to think it has no place at work."

Williams, however, is aware that not everyone agrees with her. She says it's an unpopular view with feminists, who believe that women who flirt in the office diminish their talent and intelligence, and with men, who feel more vulnerable to sexual harassment suits. To the critics, she says: "It's empowering. Flirting is one of many assets that you can work to get ahead."

"It's a touchier topic from the male perspective," weighs in Shawn Graham, author of "Courting Your Career: Match Yourself with the Perfect Job." He believes this strategy can be risky because the success of flirtation largely depends on how it's received. Most women, or men for that matter, don't want to express literal romantic interest or be seen as the "office flirt." So it involves subtlety. "Platonic flirtation can be a great way to build relationships and rapport with coworkers," Graham concludes.

Williams describes professional flirtation like an extension of good networking skills. Many of the same rules apply: Maintain eye contact, smile, show interest by asking questions, listen. Then comes a dash of flirtatious nuance. Williams defines flirting as an effort to make the other person feel confident and attractive (the dictionary definition isn't far off: "to behave amorously without serious intent"), so she also advises giving an authentic compliment or offering a touch on the hand.

One recent law grad put the theory to test. Earlier this year, Samantha, 25, had been feverishly applying for summer internships on Wall Street to no avail. She couldn't seem to get any second-round interviews. A friend suggested they go to happy hour at a bar in New York's financial district and try to network. It was packed with men, so Samantha decided to turn up the charm. She flirted with a few of the bankers. She made eye contact, asked them questions about themselves, leaned in to show her interest and laughed, a lot.

It worked. She secured a follow-up coffee meeting with a high-ranking man in the banking industry who helped her land a prestigious summer associate position at his company. While in the job, she's continued to use some of the tactics with coworkers in the hopes of making inroads to a full-time position. "It can be a great tool for women, if you can back it up with knowledge and experience," she says. "It helped me get my foot in the door, but don't think you can go in with nothing else and flirt your way to a job."

Besides, all well-intentioned flirting can easily backfire, Graham cautions. He advises that you err on the side of conservatism and know your audience. "Read how people react to you," he says. "It can be dangerous if the person reacts the wrong way."

Williams learned this firsthand. Early in her career, she crossed the line. She'd been in a meeting with superiors, frequently emphasizing points by touching one on the hand. Later, the group went out for dinner and drinks. When she came out of the restroom, one of the men cornered her and said, "I'll give you something to touch."

Looking back, she says, "Over dinner and drinks, I should have stopped touching." Now she warns others to pay careful attention to how your actions are being received. If the other person is uncomfortable or seriously interested, back away.

Heather Owen practices employment law as a partner at Constangy, Brooks & Smith in Jacksonville, Fla. She says if you're flirting to get ahead, you're usually dealing with a superior, so the chances of being pinned by a sexual harassment suit are unlikely. However, she fervently warns against any supervisor attempting to flirt with someone below them. "Using any authority to assist with harassment results in the company being liable."

Owen notes, too, that junior employees still need to be cautious. "The definition of legal harassment is unwelcome conduct of a sexual nature," she explains. "When somebody is flirtatious, it indicates a welcomeness back." In other words, if your actions are misunderstood and suddenly you become the victim of harassment, earlier examples of flirtatious behavior may make you seem complicit.

"Flirting is one of the most strategic tools you have, but there is a risk," Williams agrees. "As soon as you make people feel uncomfortable or there's a power imbalance, back off. That's the law."